Based on the type of connector, I am more likely to think these are data lines rather than ones that transmit power. Chances are this power supply is smarter than just "turn power to max always." The SoC (M2 chip) or other components on the logic board may want to know information about how much power is being provided, or temperature information, or any number of things. My guess is that the power supply only provides 12V power. 5V and 3V are likely derived on the board itself.
iMac Power Supplies function this way as well, and also typically have a separate cable that carries data